1. Field of the Invention
The present invention relates to a method of producing expanded thermoformable materials and, more particularly, to an energy efficient method for continuously producing expanded thermoformable materials.
2. Description of the Prior Art
Processes used to make expanded thermoformable materials typically involve placing a thermoformable polymeric material blank between mold plates, which are attached to a heated press. The thermoformable polymeric material blank is heated to a temperature at which the thermoformable material will adhesively bond with the mold plates by hot tack adhesion. The mold plates are than separated apart with the thermoformable material still adhered to the mold plates so as to effect an expansion of the cross-section of the thermoformable material.
Typically, the surfaces of the mold plates that are bonded to the thermoplastic material blank have a plurality of perforations thereon. The thermoplastic material will adhesively bond to the non-perforated portion of this surface so that when the mold plates are separated apart a plurality of cells will be formed within the cross-section of the expanded thermoformable material. Generally, these perforations can have a variety of different geometries and can be arranged in an array of patterns on the surface of the mold plates, thereby creating thermoformable materials having a variety of cross-sectional geometries Such methods for expanding thermoformable materials are set forth in U.S. Pat. No. 4,113,909 (Beasley), issued Sep. 12, 1978, U.S. Pat. No. 4,164,389 (Beasley), issued Aug. 14, 1979, U.S. Pat. No. 4,315,051 (Rourke), issued Feb. 9, 1982, U.S. Pat. No. 4,269,586 (Ronayne), issued May 26, 1981, U.S. Pat. No. 4,264,293 (Rourke), issued Apr. 28, 1981, and U.S. Pat. No. 4,315,050 (Rourke), issued Feb. 9, 1982, each of which is incorporated herein by reference.
The problem with these processes is that the manufacturing personnel must wait approximately fifteen to twenty minutes until the expanded thermoformable material has cooled off before they can remove it from the press and insert a new thermoformable blank. Thus, the cost of production is increased because the manufacturing personnel must wait long periods of time before each new thermoformable material blank can be inserted into the press.
Another disadvantage is that if expanded thermoformable materials with different cross-sectional geometries is desired, than the mold plates must be replaced in the press to produce the desired product. This causes several problems. First, the manufacturing personnel must wait for the previous expanded thermoformable material product to cool off so that it can be removed. Second, they must also wait for the entire press to cool off so that it reaches a safe temperature before the manufacturing personnel can again work with the press. The mold plates can be heated to temperatures in excess of 300.degree. C., which creates dangerous conditions if the manufacturing personnel are not cautious. If they attempt to remove the mold plates before they are completely cooled off, grave injuries or even death could occur. Thus, the cost of production is increased if a variety of expanded thermoformable materials are desired because of the additional time and precautions which the manufacturing personnel must take when replacing the mold plates.
Another disadvantage is that the thermoplastic material is heated and cooled in the same zone. Each thermoformable material sheet that is to be expanded must be heated in the press from room temperature to the temperature at which the material will exhibit hot tack adhesion. Thus, additional time is required because the thermoplastic material sheet is not pre-heated prior to its insertion into the press.
In addition, the cost of production is substantially increased because of the a mount of wasted energy in these conventional processes. Each thermoformable material must be reheated using new energy due to the fact that the press must be cooled to near room temperature prior to removal of expanded thermoformable material and insertion of a new sheet of thermoformable material. Thus, the cost of production is increased because new energy must be purchased to heat each new sheet of thermoformable material that is to be expanded and all of such energy is wasted during the cooling process.
Furthermore, another disadvantage is that the processes described above are neither automated nor continuous, and typically require multiple manufacturing personnel to produce one expanded thermoformable product. Obviously, the use of multiple personnel greatly increases the cost of manufacturing, together with the long product cycle times and energy loss.
Accordingly, there is a need for an improved method of continuously producing expanded thermoformable materials that avoids the aforementioned disadvantages. In this regard, the present inventor has developed a unique continuous process, which substantially reduces product cycle time, labor costs and energy consumption. That is, only one member of the manufacturing team is required for loading and unloading of the thermoplastic material.